Noninvasive quantification of energy transfer during mechanical ventilation

Ventilator-to-patient energy transfer during insufflation (ET_v) is increasingly recognized as a potential contributor to ventilator-induced lung injury. Current formulations of ET_v, however, neglect patient-generated respiratory muscle effort (P_mus), a potentially important modifier of ventilator energy delivery. Accordingly, the aim of this study was to develop and validate mathematical expressions that quantify breath-by-breath ETv in the presence of respiratory effort using only airway pressure (P_aw) and flow (F_aw) signals. Equations were derived from the single-compartment model of the respiratory system relating the pressure-time product of respiratory muscle pressure (P_musPTP) to ET_v during volume-controlled (VCV) and pressure-controlled ventilation (PCV). Model validation was performed using previously acquired high-fidelity P_aw and F_aw recordings from two separate cohorts of invasively ventilated patients receiving VCV or PCV. Calculated ET_v values were compared with those measured by trapezoidal integration of inspiratory pressure-volume loops. There was excellent agreement between calculated and measured ETv in both modes of ventilation (VCV: R² = 0.99; bias 0.3 ± 0.9 J·min^-1; PCV: R² = 0.98; bias -0.10 ± 1.94 J·min^-1). These results demonstrate that ventilator-to-patient energy transfer during controlled mechanical ventilation can be quantified accurately and noninvasively on a breath-by-breath basis using airway signals alone. The developed model also provides a physiological basis for real-time assessment of insufflation energy dynamics.NEW & NOTEWORTHY This study presents and validates a noninvasive method that uses only airway pressure and flow signals to dynamically quantify energy transfer to mechanically ventilated patients while accounting for respiratory effort. Equations derived from a classic one-compartment model accurately predicted individual breath energy transfer during volume- and pressure-controlled ventilation. The method provides a physiological framework to explore, in real-time and non invasively, the dynamics and clinical significance of ventilator-to-patient energy transfer.